A common type of metallic convenience closure comprises a panel with an endless score line forming a central removable portion and a peripheral fixed portion that is attached to the cylindrical container. A pull-tab having a nose portion is fastened to the removable portion by a rivet so that when the pull-tab is manually grasped, the nose portion of the pull-tab moves into position adjacent the score line severing the panel. Further movement of the pull-tab completes the severing to remove the removable portion. Typical patents showing such construction are U.S. Pat. Nos. 3,696,961, 3,819,083 and 3,986,632.
Such closures are effective for the intended purpose but do require various manipulations in the manufacture that increase the cost.
However, they are not 100% safe. If the user of the product in the can moves his hand or finger with a circular motion when in contact with the panel remaining on the can, a cut will occur.
It also has been suggested that a closure be provided which has an opening that is closed by a panel which can be removed or broken as shown, for example, in U.S. Pat. Nos. 3,245,576, 3,274,962, 3,380,662, 3,547,305, 4,253,584 and 3,628,689. A major difficulty with respect to such closures is that the free edge of the metal closure is exposed to the contents and depending upon the contents is a point of incipient corrosion and contamination of the contents.
In the copending patent application Ser. No. 640,134, filed Aug. 13, 1984, there is disclosed and claimed a metallic closure comprising a central panel including means forming a part of the panel for attaching the closure to the end of a container to close the end. The panel has an opening therein and the portion of the metal adjacent the opening is rolled so that the end thereof engages under the inner surface of the panel in a smooth roll such that the free edge is not directly exposed to the contents of the container on which the closure is placed. A composite panel comprising a plurality of layers including a plastic layer is bonded to the central panel on the outer surface of the central panel by heat fusion. One of the problems in the manufacture of such a closure is that the pull-tab which is formed integrally with a composite panel and folded back onto the surface of the composite panel tends to adhere during heat fusion to the apparatus which is folding the tab.
Accordingly, among the objectives of the present invention are to provide a metal closure of the aforementioned type wherein the tab will not adhere to the apparatus and to provide a novel method and apparatus for forming such a closure.
In accordance with the invention, the metallic closure for a cylindrical, rectangular or square container comprises a central panel which has a portion thereof adapted for attaching the closure to the end of a container to close the end. The panel has an opening therein and the portion of the metal adjacent the opening is rolled so that the end thereof engages under the inner surface of the panel in a smooth roll such that the free edge is not directly exposed to the contents in the container on which the closure is placed. A composite panel including a layer of plastic is bonded to the central panel and the outer surface of the central panel by heat fusion of plastic. The composite panel includes a tab that is formed integrally thereof and initially is folded back upon itself bringing the surfaces of the tab which bear the plastic into contact so that the two portions of the tab are bonded to one another to provide a double strength tab.